The present invention relates generally to polymer-clay nanocomposites comprising a matrix polymer and a layered clay material having an improved level of extractable materials. The polymer-clay nanocomposites comprising the layered clay material may be processed under normal conditions while providing low haze and improved oxygen barrier properties. This invention further relates to articles produced from the polymer-clay nanocomposites and processes relating to the nanocomposites.
Thermoplastic materials are being increasingly used in the packaging of beverages and perishable foods. Plastics are often the material of choice for food and beverage packaging because of their clarity, flexibility, toughness, gas barrier properties, lighter weight, processability and high gloss. Polymer nanocomposites comprising a layered clay material having platelet particles dispersed therein have the potential for improved properties, including increased gas barrier, heat deflection temperature, and modulus.
Nevertheless, platelet particles derived from layered clay materials dispersed in a polymer nanocomposite may also induce crystallization and void formation during melt processing operations, such as the stretching or orientation of films. This may lead to very high levels of haze, and/or degradation of the gas barrier properties of the films made from nanocomposite materials, which renders the nanocomposites less desirable for food packaging applications, for example. Similar phenomena observed during the use of prior art nanocomposite materials in stretch blow molding applications can even lead to void and hole formation in the polymer films, which generally minimizes the usefulness of these compositions in high barrier applications.
Certain salts of organic cations have been used in the prior art to intercalate and/or cation exchange the layered clay materials used to make the nanocomposites. It has been taught in the prior art to use excess quantities of the salts of the organic cations when intercalating the layered clay material to facilitate complete cation exchange in the layered clay material, and thereby facilitate dispersion of the clay into various carrier materials to provide the desired individual platelet particles. As a result, intercalated layered clay materials in the prior art may be contaminated with the salts of the organic cations used as starting materials to intercalate and/or ion-exchange the layered clay material. It would be beneficial for some applications to provide an intercalated layered clay material with improved levels of certain extractable materials, such as extractable salts of organic cations.
The present invention is generally related to polymer-clay nanocomposites. The nanocomposites and/or intercalated layered clay materials of this invention result in improved physical properties as a result of the incorporation therein of a layered clay material comprising platelet particles. The layered clay material may be treated or modified with an organic cation to form an organoclay. A reduced level of permeability of gases, such as oxygen and carbon dioxide, through the nanocomposite material, and improved transparency of the nanocomposite may be achieved by employing a layered clay material having an improved level of certain extractable materials, such as certain salts of organic cations that are used to prepare the layered clay material.
Additional advantages of the invention will be set forth in part in the detailed description, which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory of preferred embodiments of the invention, and are not restrictive of the invention, as claimed.